The present invention relates to a phase change memory device and a method of manufacturing the same, and, more particularly, to a phase change memory device, which enhances the current driving capability of switching elements, and to a method of manufacturing the same.
Recently, a considerable amount of research has been conducted in the hopes of developing novel memory devices that have simple configurations capable of achieving high levels of integration while retaining many if not all of the characteristics of present day non-volatile memory devices. One group of novel memory devices studied is the phase change memory devices.
Phase change memory devices are those types of memory devices that exploit a change in a physical property, e.g., usually resistance, which reversibly changes as a function of the particular phase of the phase change layer material. Phase change memory devices are usually constructed of a phase change material interposed between two opposing electrodes. Phase change materials are often those types of materials that reversibly change between an ordered crystalline solid state to a disordered amorphous solid state as a function of a rate of heating, cooling or annealing which is usually initiated by flowing an electrical current between two opposing electrodes. Digital information can be stored in these types of memory cells by measuring the magnitude of these variable physical properties, e.g., a variable resistance, which changes as a function of which state the phase change layer is in.
Development of the phase change memory device should also take into consideration the important factor that the electrical currents used to drive the phase changes, i.e., the programming currents, should be minimized. Accordingly, recent phase change memory devices include vertical PN diodes instead of transistors as cell switching elements. The reason for doing this is that vertical PN diodes have a higher current flow densities than those of transistors. Therefore use of vertical PN diodes in the design of phase change memory devices may reduce the programming current and the cell size, and thereby may be advantageously applied to furthering higher integration of the phase change memory device.
It should also be noted that the current driving properties of the PN diodes are affected by the purity of the material properties of the diodes and peripheral resistance values of the diodes. Typically, peripheral resistance affecting the current driving properties of the PN diodes may include resistance of a silicon substrate and word line contact resistance.
Accordingly, to manufacture the phase change memory devices that use PN diodes in their design it is very important to control the peripheral resistance of the diodes which can adversely affect, i.e., reduce, the current driving performance of the PN diodes. Accordingly, in order to reduce the peripheral resistance of the PN diodes, when the conventional phase change memory device is manufactured, an ion-implanting process for doping a silicon substrate with a dopant may be performed. However, the ion-implanting process has its physical limitations in terms that it can only reduce the resistance of the subsequent silicon substrate to about 90 Q or less.